Circuit board capable of preventing electrostatic breakdown and magnetic head using the same

ABSTRACT

The invention provides a magnetic head capable of positively preventing electrostatic breakdown of an MR magnetic head device, and a method of manufacturing the magnetic head. A circuit board comprises at least a pair of leads for constructing a circuit, lands connected respectively to the leads, and solder bumps formed respectively on the lands. The solder bumps are arranged in an adjacent relationship and, when the solder bumps are crushed, peripheral portions of the solder bumps are pressed or spread so as to overlap with each other. The magnetic head includes the circuit board.

This application is a division of application Ser. No. 09/629,804, filedJul. 31, 2000, which is hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a circuit board, and a magnetic headincorporating the circuit board. More particularly, the presentinvention relates to a circuit board capable of protecting an MRmagnetic head device, which incorporates the circuit board, againstelectrostatic breakdown.

2. Description of the Related Art

An example of a conventional magnetic head 201 for use in a computerhard disk is shown in FIG. 17. The magnetic head 201 generally comprisesa slider 203, a load beam 202, and a circuit board 204. The slider 203is attached to a fore end 202 a of the load beam 202 through a flexure,and a base plate 209 is attached to an opposite end 202 b of the loadbeam 202. The circuit board 204 is attached to the base plate 209.

The slider 203 includes an MR magnetic head device 208 for reproducingmagnetically recorded data, and an inductive head device (not shown) forrecording data to be magnetically recorded. From each of these headdevices, two lead lines are extended to transmit and receive areproduced signal and a recording signal to and from the outside of themagnetic head. These four lead lines 205 a, 205 b, 206 a, 206 b areconnected to the circuit board 204 at the side of the base plate 209where it is attached to the opposite end 202 b of the load beam 202.

The circuit board 204 is formed of a flexible printed board, andincludes four leads 215 a, 215 b, 216 a, 216 b connected respectively tothe lead lines extended from the head devices (i.e., 205 a, 205 b, 206a, 206 b). Mounting terminals 215 c, 215 d, 216 c, 216 d are providedrespectively midway on the leads 215 a, 215 b, 216 a, 216 b. Inspectionterminals 215 e, 215 f, 216 e, 216 f are provided respectively at endsof the leads 215 a, 215 b, 216 a, 216 b.

The leads 215 a, 215 b, that are connected to the lead lines 205 a, 205b of the MR magnetic head device 208, include lands 223, 224 providedbetween the mounting terminals 215 c, 215 d and the inspection terminals215 e, 215 f, respectively.

In a conventional magnetic head of this type, the circuit including theMR magnetic head device 208 is typically constructed as a closed circuitby attaching a shunt clip or forming a bonding wire between the lands223, 224 so as to short the lands 223, 224 together. This is done toprevent electrostatic breakdown of the MR magnetic head device 208during a period from manufacture of the magnetic head to assemblythereof into a hard disk drive.

This may result in a number of problems. For example, when the lands223, 224 are shorted together by using a clip, there is a risk that theclip may slip off as result of vibration during transport of themagnetic head. As a result, the MR magnetic head device 208 may sufferelectrostatic breakdown.

Also, shorting the lands 223, 224 together by wire bonding requires thata wire-bonding step be included in the manufacturing process of themagnetic head, thereby resulting in an increased production cost of themagnetic head.

In view of the state of the art set forth above, an object of thepresent invention is to provide a magnetic head capable of positivelypreventing electrostatic breakdown of an MR magnetic head device, and amethod of manufacturing the magnetic head, that overcomes theabove-identified problems.

SUMMARY OF THE INVENTION

The present invention is directed to a circuit board comprising at leasta pair of leads for constructing a circuit, lands connected respectivelyto the pair of leads, and solder bumps formed respectively on the lands,wherein the solder bumps are arranged in an adjacent relationship. Thesolder bumps are subsequently crushed, causing peripheral portions ofthe solder bumps to spread and overlap with each other.

The present invention is also directed to a circuit board comprising atleast a pair of leads for constructing a circuit, lands formed forconnection respectively to the pair of leads, and a solder bridge forelectrically interconnecting the lands, wherein the solder bridge isformed by peripheral portions of the solder bumps formed on the lands sothat portions of the solder bumps overlap with each other. Preferably,the solder bridge is formed by crushing the solder bumps formed on thelands to an extent that crushed peripheral portions of the solder bumpsare overlapped with each other.

Consequently, the leads constructing the circuit on the circuit boardcan be easily shorted together by crushing the solder bumps, and thecircuit can be formed into a closed circuit.

Moreover, since the solder bridge is formed by the peripheral portionsof the solder bumps which are integrally overlapped with each other, thecontact area between the solder bumps is increased and the leads can bepositively shorted between them.

Further, the present invention is directed to a circuit shorting methodfor a circuit board comprising at least a pair of leads for constructinga circuit, lands connected respectively to the pair of leads, and solderbumps formed on the lands and positioned adjacent to each other. Themethod comprises the steps of crushing one of the solder bumps such thata peripheral portion of the one solder bump is pressed to spread outwardin a radial direction to approach the other solder bump; and thencrushing the other solder bump such that a peripheral portion of theother solder bump is pressed to spread outward in a radial direction tocontact with the peripheral portion of the one solder bump, whereby thepair of leads are shorted.

With this circuit shorting method, two solder bumps are contacted witheach other by crushing the solder bumps one by one. Therefore, thesolder bumps can be each positively crushed to make the leads shortedbetween them, and the circuit can be positively formed into a closedcircuit.

In the above circuit shorting method, the step of crushing the othersolder bump is preferably performed until a part of the peripheralportion of the other solder bump overlaps the peripheral portion of theone solder bump.

One feature of this circuit shorting method is that the pair of solderbumps are contacted with each other in an overlapping relation. Thus,the solder bumps are unlikely to be separated, even when the circuitboard is bent or flexed. Further, a contact area between the solderbumps is increased and the pair of leads can be positively shortedbetween them.

In the above circuit shorting method, the solder bumps are preferablyeach crushed under heating. Heating of the solder bumps causes them tosoften, thereby reducing the load required for crushing the solderbumps, and the solder bumps can be positively crushed without damagingthe circuit board itself.

In the above circuit shorting method, the pair of solder bumps may becrushed simultaneously underheating. Crushing the solder bumpssimultaneously, while being softened under heating, reduces the loadrequired for crushing the solder bumps, and the pair of solder bumps canbe positively contacted with each other even when they are crushedsimultaneously. Additionally, damage of the circuit board itself can beavoided.

In the above circuit shorting method, the solder bumps are preferablyeach crushed under heating and rubbing. By heating and rubbing thesolder bumps, each solder bump is caused to spread in the planardirection of the circuit board while being crushed. This causes thesolder bumps to be more positively contacted with each other.

The present invention is directed to a magnetic head in which a sliderincluding an MR magnetic head device is attached to a fore end of a loadbeam, a circuit board is attached to an opposite end of the load beam,and a pair of lead lines extended from the MR magnetic head device areconnected to the circuit board. The circuit board comprises at least apair of leads connected respectively to the lead lines and constructinga circuit including the MR magnetic head device in cooperation with thelead lines, lands connected respectively to the leads, and solder bumpsformed respectively on the lands. The solder bumps are arranged in anadjacent relationship and, when the solder bumps are crushed, peripheralportions of the solder bumps are pressed to spread and overlap with eachother.

The present invention is also directed to a magnetic head in which aslider including an MR magnetic head device is attached to a fore end ofa load beam, a circuit board is attached to an opposite end of the loadbeam, and a pair of lead lines extended from the MR magnetic head deviceare connected to the circuit board. The circuit board comprises at leasta pair of leads connected respectively to the lead lines andconstructing a circuit including the MR magnetic head device incooperation with the lead lines, lands connected respectively to theleads, and a solder bridge for electrically interconnecting the lands.The solder bridge is formed by peripheral portions of the solder bumpsformed respectively on the leads and overlapped with each other. Thesolder bridge is preferably formed by crushing the solder bumps formedon the lands to an extent that crushed peripheral portions of the solderbumps are overlapped with each other.

With respect to the MR magnetic head device, a circuit is constructedwith the lead lines extended from the head device and the pair of leadsconnected to the lead lines. The circuit can be easily formed into aclosed circuit by crushing the solder bumps so that the pair of leadsare shorted between them. As a result, the MR magnetic head device canbe protected against electrostatic breakdown.

The present invention is directed to a method of manufacturing amagnetic head in which a slider including an MR magnetic head device isattached to a fore end of a load beam and a circuit board is attached toan opposite end of the load beam. The circuit board comprises at least apair of leads connected to the MR magnetic head device, lands connectedrespectively to the pair of leads, and solder bumps formed respectivelyon the lands and positioned adjacent to each other The method comprisesthe steps of crushing one of the solder bumps such that a peripheralportion of the one solder bump is spread outward in a radial directionto approach the other solder bump; and then crushing the other solderbump such that a peripheral portion of the other solder bump is likewisespread outward in a radial direction to contact with the peripheralportion of the one solder bump, whereby the pair of leads are shorted.

With this method of manufacturing a magnetic head, a circuit isconstructed by the MR magnetic head device, the lead lines extended fromthe head device and the pair of leads connected to the lead lines. Thecircuit is formed into a closed circuit by crushing the solder bumps sothat the pair of leads are shorted between them. Therefore, the MRmagnetic head device can be protected against electrostatic breakdown.

In the above method of manufacturing a magnetic head, the step ofcrushing the other solder bump is preferably performed until a part ofthe peripheral portion of the other solder bump overlaps the peripheralportion of the one solder bump. Since the pair of solder bumps arecontacted with each other in an overlapping relationship, the contactarea between the solder bumps is increased and the pair of leads can bemore positively shorted together, whereby the circuit including the MRmagnetic head device can be formed into a closed circuit.

In the above described method of manufacturing a magnetic head, thesolder bumps are each preferably crushed under heating. Heating softensthe solder bumps, thereby reducing the load required for crushing thesolder bumps, and the solder bumps can be crushed without damaging thecircuit board itself.

In the above described method of manufacturing a magnetic head, the pairof solder bumps may be crushed simultaneously under heating. Crushingthe solder bumps simultaneously while they are being softened underheating, reduces the load required for crushing the solder bumps, andthe pair of solder bumps can be positively contacted with each othereven when they are crushed simultaneously. Damage of the circuit boardcan consequently be avoided.

In the above described method of manufacturing a magnetic head, thesolder bumps are each preferably crushed under heating and rubbing. Byheating and rubbing the solder bumps as they are each crushed, eachsolder bump is spread in the planar direction of the circuit board whilebeing crushed, which causes the solder bumps to be more positivelycontacted with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a magnetic head according to anembodiment of the present invention;

FIG. 2 is a plan view showing a principal part of a circuit boardprovided on the magnetic head shown in FIG. 1;

FIG. 3 is a sectional view of the principal part of the circuit boardshown in FIG. 2;

FIG. 4 is a plan view showing the principal part of the circuit boardprovided on the magnetic head shown in FIG. 1;

FIG. 5 is a sectional view of the principal part of the circuit boardshown in FIG. 4;

FIG. 6 is a sectional view depicting a step of a method of manufacturingthe magnetic head according to an embodiment of the present invention;

FIG. 7 is a sectional view depicting a step of a method of manufacturingthe magnetic head according to the embodiment of the present invention;

FIG. 8 is a sectional view depicting a step of a method of manufacturingthe magnetic head according to the embodiment of the present invention;

FIG. 9 is a sectional view depicting a step of a first alternativemethod of manufacturing the magnetic head according to an embodiment ofthe present invention;

FIG. 10 is a sectional view depicting a step of the first alternativemethod of manufacturing the magnetic head according to the embodiment ofthe present invention;

FIG. 11 is a sectional view depicting a step of the first alternativemethod of manufacturing the magnetic head according to the embodiment ofthe present invention;

FIG. 12 is a sectional view depicting a step of a second alternativemethod of manufacturing the magnetic head according to an embodiment ofthe present invention;

FIG. 13 is a sectional view depicting a step of the second alternativemethod of manufacturing the magnetic head according to the embodiment ofthe present invention;

FIG. 14 is a graph showing changes in the diameter of a solder bump whenthe solder bump is crushed pursuant to an embodiment of the presentinvention;

FIG. 15 is a graph showing changes in the diameter of a solder bump whenthe solder bump is crushed pursuant to an embodiment of the presentinvention;

FIGS. 16a-d are schematic views showing a pair of solder bumps insuccessive states when crushed pursuant to an embodiment of the presentinvention;

FIG. 17 is a perspective view of a conventional magnetic head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings.

FIG. 1 shows a magnetic head 1 according to the present invention. Themagnetic head 1 mainly comprises a load beam 2, a slider 3 attached to afore end 2 a of the load beam 2, and a circuit board 4 of the presentinvention attached to a base plate 9. The base plate 9 is attached to abase (opposite) end 2 b of the load beam 2.

The slider 3 includes an MR magnetic head device 8 serving as areproducing head and an inductive head device (not shown) serving as arecording head, these head devices being provided on one end surface ofthe slider 3.

One pair of lead lines 5 a, 5 b are extended from the MR magnetic headdevice 8, and another pair of lead lines 6 a, 6 b are extended from theinductive head device.

The lead lines 5 a, 5 b, 6 a, 6 b are collected together by a flexibleprinted circuit (FPC) board 7 on the upper surface of the load beam 2.The FPC board 7 extends to the base plate 9 (attached to the oppositeend 2 b of the load beam 2).

The circuit board 4 is connected to the FPC board 7 through connectionterminals 17 a, 17 b, 18 a, 18 b. The circuit board 4 is attached to thebase plate 9 in an overlapped relationship to an end portion of the FPCboard 7.

The circuit board 4 of the present invention comprises, as shown inFIGS. 1 to 3, a substrate 21 and an insulating layer 22 formed over thesubstrate 21. Four leads 15 a, 15 b, 16 a, 16 b are formed on thesubstrate 21 and are covered by the insulating layer 22. Also, as shownin FIG. 1, the leads 15 a, 15 b, 16 a, 16 b are connected to theconnection terminals 17 a, 17 b, 18 a, 18 b, respectively.

Further, as shown in FIG. 1, the leads 15 a, 15 b, 16 a, 16 b includemounting terminals 15 c, 15 d, 16 c, 16 d and inspection terminals 15 e,15 f, 16 e, 16 f provided thereon.

At the juncture (i.e., overlapped portion) between the circuit board 4and the FPC board 7, the connection terminals 17 a, 17 b, 18 a, 18 b ofthe circuit board 4 are connected respectively to four connectionterminals (not shown) of the FPC board 7.

As set forth in the above-described arrangement, the lead 15 a isconnected to the lead line 5 a through the connection terminal 17 a, andthe lead 15 b is connected to the lead line 5 b through the connectionterminal 17 b. Similarly, the lead 16 a is connected to the lead line 6a through the connection terminal 18 a, and the lead 16 b is connectedto the lead line 6 b through the connection terminal 18 b.

Thus, the MR magnetic head device 8, the lead lines 5 a, 5 b and theleads 15 a, 15 b cooperatively construct or form a circuit.

Lands 23, 24 are formed on the leads 15 a, 15 b (which forms the circuitincluding the MR magnetic head device 8) between the mounting terminals15 c, 15 d and the inspection terminals 15 e, 15 f, respectively, asshown in FIGS. 2 and 3. Solder bumps 25, 26, being substantiallycircular in plan view, are formed on the lands 23, 24, respectively. Thelands 23, 24 are formed as conductors positioned on the leads 15 a, 15b, and projecting through the insulating layer 22. The solder bumps 25,26 are formed respectively on the lands 23, 24 and are electricallyconnected to the leads 15 a, 15 b.

In the preferred embodiment, the solder bumps 25, 26 are formed from asolder made of, e.g., an SnPb alloy, and has a melting point preferablyin the range of about 180° C.-185° C., taking into account that thesolder bump is required to be easily crushed.

The solder bumps 25, 26 are preferably arranged adjacent to each otherand with a distance left between them that, when crushed, theirperipheral portions 25 a, 26 a are spread outward in the radialdirection to allow interconnection between the solder bumps 25 and 26.More specifically, assuming that the solder bumps 25, 26 each have adiameter of 0.29-0.34 mm, the center-to-center distance between thesolder bumps 25 and 26 is preferably in the range of 0.39-0.41 mm. Ifthe center-to-center distance is less than 0.39 mm, there is a risk thatthe solder bumps 25, 26 may contact with each other when they areformed. Conversely, if the center-to-center distance is more than 0.41mm, there is a risk that the solder bumps 25, 26 may not contact witheach other even after they are crushed.

FIGS. 4 and 5 show the solder bumps 25, 26 of the circuit board 4 afterbeing crushed according to the present invention. When the solder bumps25, 26 are crushed, the peripheral portions 25 a, 26 a of the solderbumps 25, 26 are caused to spread into an integrally overlappedrelationship, thereby forming a solder bridge 125. The solder bridge 125electrically connects the lands 23, 24 to each other for the purpose ofshorting the leads 15 a, 15 b together so that the circuit including theMR magnetic head device 8 is formed into a closed circuit.

A method of manufacturing the magnetic head of the present inventionwill now be described with reference to the drawings.

First, the slider 3, including the MR magnetic head device 8 and theinductive head device (not shown), is attached to the fore end 2 a ofthe load beam 2. The lead lines 5 a, 5 b, 6 a, 6 b are extended from theMR magnetic head device 8 and the inductive head device up to the baseend 2 b of the load beam 2 through the FPC board 7.

Then, the circuit board 4 is attached to the base end 2 bof the loadbeam 2. At this time, the lead lines 5 a, 5 b, 6 a, 6 b are connected tothe leads 15 a, 15 b, 16 a, 16 b, respectively, of the circuit board 4through the connection terminals 17 a, 17 b, 18 a, 18 b. Accordingly,the MR magnetic head device 8, the lead lines 5 a, 5 b and the leads 15a, 15 b are interconnected to form or construct a circuit.

Then, as shown in FIG. 6, a pressing tip 30 is prepared and pressedagainst the first solder bump 25, whereupon the solder bump 25 iscrushed as shown in FIG. 7. As a result of this crushing, the peripheralportion 25 a of the solder bump 25 is pressed or spread outward in theradial direction so as to approach the other or second solder bump 26.

Then, as shown in FIG. 8, the pressing tip 30 is pressed against theother or second solder bump 26, whereupon the solder bump 26 is crushed.The peripheral portion 26 a of the solder bump 26 is thereby pressed orspread outward in the radial direction until the peripheral portion 26 aoverlaps the peripheral portion 25 a of the first solder bump.

When the solder bumps 25, 26 contact with each other, the leads 15 a, 15b are shorted together or between them and the circuit including the MRmagnetic head device 8 is formed into a closed circuit.

An alternative method for crushing the solder bumps 25, 26 is shown inFIGS. 9-11. Instead of the pressing tip 30 (as described above), aheater tip 33 comprising a heat-resistant resin film 31 and a heater 32attached to the film 31 is utilized. The heater tip 33 is pressedagainst the first solder bump 25 while heating the same, whereupon thesolder bump 25 is crushed as shown in FIG. 10. As a result of thecrushing, the peripheral portion 25 a of the solder bump 25 is pressedor spread outward in the radial direction so as to approach the other orsecond solder bump 26.

Then, as shown in FIG. 11, the heater tip 33 is pressed against theother or second solder bump 26 while heating the same, whereupon thesolder bump 26 is crushed. The peripheral portion 26 a of the solderbump 26 is thereby pressed or spread outward in the radial directionuntil the peripheral portion 26 a overlaps the peripheral portion 25 aof the first solder bump 25.

As the solder bumps 25, 26 contact each other, the leads 15 a, 15 b areshorted together or between them, and the circuit including the MRmagnetic head device 8 is formed into a closed circuit.

In the case of crushing the solder bumps 25, 26 by the heater tip 33, itis preferable that the heating temperature of the solder bumps 25, 26 beset to 170-210° C., and more preferably 175-185° C. The preferredheating time is 1.5-2.5 seconds, and more preferably 1.5-2.0 seconds.

If the heating temperature is lower than 170° C., then the solder maynot be sufficiently softened, thereby preventing the solder bumps 25, 26from contacting with each other, or that a too large of a load must beapplied to crush the solder bumps 25, 26, which can cause the circuitboard 4 to be damaged. If the heating temperature is higher than 210°C., then there is a risk that the solder bumps 25, 26 are completelymelted into a liquid state, and when crushed, parts of the solder mayscatter around the solder bumps 25, 26 upon collapse of the bump shapes.

Further, if the heating time is shorter than 1.5 seconds, there is arisk that the solder will not be sufficiently softened to permit thesolder bumps 25, 26 to contact with each other upon crushing. If theheating time is longer than 2.5 seconds, then there is a risk that thesolder bumps 25, 26 will completely melted into a liquid state, and whencrushed, parts of the solder may scatter around the solder bumps 25, 26upon collapse of the bump shapes.

Another alternative method for crushing the solder bumps 25, 26 is shownin FIGS. 12-13. A pressing tip 35 that is larger than the pressing tip30 described above is utilized in conjunction with a heater 34. Theheater 34 is held in contact with the underside of the circuit board 4to heat the solder bumps 25, 26. The pressing tip 35 is positioned abovethe circuit board 4. Then, as shown in FIG. 13, both the solder bumps25, 26 are crushed simultaneously by the pressing tip 35 while they areheated from below with the heater 34.

In this case, the peripheral portion 25 a of one solder bump 25 and theperipheral portion 26 a of the other solder bump 26 are simultaneouslypressed or spread outward in the radial direction so as to approach andcontact with each other. As the solder bumps 25, 26 contact with eachother, the leads 15 a, 15 b are shorted together or between them and thecircuit including the MR magnetic head device 8 is formed into a closedcircuit.

When crushing the solder bumps 25, 26 by the larger pressing tip 35 andthe heater 34, the heating temperature and the heating time arepreferably set in accordance with the above-described methods.

Moreover, when crushing the solder bumps 25, 26 by any of theabove-described methods (i.e., with the pressing tip 30, the heater tip33, or the combination of the pressing tip 35 and the heater 34, asshown in FIGS. 6 to 13), the solder bumps 25, 26 are preferably crushedwhile the tips 30, 33, or 35 are moved in a rubbing fashion with respectto the solder bumps in the planar direction of the circuit board 4. Thisrubbing improves or increases the spreading of the solder bumps 25, 26in the planar direction of the circuit board 4 during the step ofcrushing, thereby increasing the positive contacted between the solderbumps 25, 26.

With the magnetic head 1 described above, the MR magnetic head device 8,the lead lines 5 a, 5 b and the leads 15 a, 15 b cooperatively constructa circuit, and one pair of the solder bumps 25, 26 connected to theleads 15 a, 15 b are crushed successively or simultaneously so as tocontact with each other. The leads 15 a, 15 b are thereby shortedbetween them to make the constructed circuit become a closed circuit. Asa result, the MR magnetic head device 8 can be protected againstelectrostatic breakdown.

With the above-described method of manufacturing the magnetic head 1,the circuit including the MR magnetic head device 8 can be easily formedinto a closed circuit by merely crushing the solder bumps 25, 26.

Also, with the above-described method of manufacturing the magnetic head1, the solder is softened by heating when the solder bumps 25, 26 arecrushed. Therefore, the load required for crushing the solder bumps 25,26 is reduced and the solder bumps 25, 26 can be positively crushedwithout damaging the circuit board 4.

Further, since the solder bumps 25, 26 are crushed to an extent that apart of the peripheral portion 26 a of the other solder bump 26 overlapsthe peripheral portion 25 a of one solder bump 25, the contact areabetween the solder bumps 25, 26 is increased and one pair of the leadscan be more positively or securely shorted together or between them. Asa result, the circuit including the MR magnetic head device 8 can beformed into a closed circuit. Since the peripheral portions 25 a, 26 aare overlapped with each other, the solder bumps 25, 26 are avoided fromseparating off, for example, even when the circuit board 4 is bent.

Furthermore, with the above-described method of manufacturing themagnetic head 1 by crushing one pair of the solder bumps 25, 26 whilebeing heated, the load required for crushing the solder bumps 25, 26 isreduced and the solder bumps 25, 26 can be positively contacted witheach other even though both the solder bumps are crushed at the sametime, without damaging the circuit board 4 when the solder bumps arecrushed.

In addition, with the above-described method of manufacturing themagnetic head 1 by crushing the solder bumps 25, 26 in a rubbingfashion, the solder bumps 25, 26 are pressed or spread in the planardirection of the circuit board 4 while being crushed and they can bemore positively contacted with each other.

EXPERIMENTAL EXAMPLE 1

A land was formed on a circuit board, and a substantially semisphericalsolder bump having a diameter of 0.32 mm (320 μm) and a maximum heightof 28 μm was formed on the land.

Further, on another circuit board, a substantially semispherical solderbump having a diameter of 0.26 mm (260 μm) and a maximum height of 25 μmwas formed in a similar manner to the above. The solder used was made ofan SnPb alloy and had the melting point of 183° C.

These solder bumps were each crushed by applying a load of 5-15 kgf, andchanges in the bump diameter were measured. Measured results are shownin FIGS. 14 and 15.

As seen from FIG. 14, the diameter of the solder bump having a diameterof 320 μm was changed to 450-490 μm after the crushing.

Also, as seen from FIG. 15, the diameter of the solder bump having adiameter of 260 μm was changed to 370-430 μm after the crushing.

It is thus understood that, when the solder bump is crushed, the bumpdiameter is increased and a peripheral portion of the solder bump ispressed or spread outward in the radial direction.

EXPERIMENTAL EXAMPLE 2

Next, a circuit board including one pair of solder bumps, as shown inFIGS. 1 to 3, was fabricated. The solder bumps each had a diameter of0.32 mm and the center-to-center distance between the solder bumps was0.4 mm. The solder used was made of an SnPb alloy and had a meltingpoint of 183° C.

First, one solder bump was crushed by heating the solder bump up to220-260° C. for 1.0-2.5 seconds, under a load of 8 kgf with a heatertip, while the heater tip was moved in rubbing fashion in the planardirection of the circuit board. The other solder bump was then crushedin a similar manner.

Continuity between both the solder bumps was subsequently checked.Checked results are listed in Table 1 and shown schematically in FIGS.16a-d. FIGS. 16a-d shows the solder bumps in successive states whencrushed while being heated to a temperature of 250° C.

As seen from Table 1 and FIG. 16a, when the heating time is 1.0 secondat the heating temperature in the range of 170-250° C., the solder bumpsare insufficiently crushed and they do not contact with each other.Thus, no electrical conduction is established between the solder bumps.

As seen from FIG. 16d, when the heating temperature is higher than 210°C. and the heating time is longer than 2.5 seconds, the soler isexcessively melted and a part of the solder is scattered around thesolder bumps.

From the above results, it is understood that in order to crush andcontact one pair of the solder bumps each having the diameter of 0.32 mmwith the center-to-center distance of 0.4 mm, the solder bumps arepreferably crushed while being heated to 170-210° C. for 1.5-2.0 seconds(see FIGS. 16b-c).

TABLE 1 Heating Time Heating Temperature (° C.) (sec) 170° C. 180° C.190° C. 200° C. 210° C. 1.0 sec no no no no no conduction conductionconduction conduction conduction 1.5 sec conduction conductionconduction conduction conduction 2.0 sec conduction conductionconduction conduction conduction 2.5 sec conduction conductionconduction conduction conduction

As fully described above, the circuit board according to the presentinvention comprises at least a pair of leads and a pair of solder bumps.The solder bumps are arranged in an adjacent relationship and, when thesolder bumps are crushed, peripheral portions of the solder bumps areoverlapped with each other. Therefore, the leads constructing a circuitcan be easily shorted together or between them by merely crushing thesolder bumps, and the circuit can be formed into a closed circuit.

Also, the circuit board according to the present invention comprises asolder bridge for electrically interconnecting lands connected to theleads, the solder bridge being formed by the peripheral portions of thesolder bumps formed on the lands, which are integrally overlapped witheach other. Therefore, the contact area between the solder bumps isincreased and the leads can be more positively shorted between them.

In addition, since the peripheral portions of the solder bumps areoverlapped with each other, separation of the solder bumps is avoided,for example, even when the circuit board is bent. Therefore, the shortedstate between the leads established by the solder bridge is maintainedand reliability of the circuit board can be increased.

The circuit shorting method according to the present invention comprisesthe steps of crushing one of the solder bumps such that a peripheralportion of the one solder bump is pressed or spread outward in theradial direction to approach the other solder bump; and then crushingthe other solder bump such that a peripheral portion of the other solderbump is pressed or spread outward in the radial direction to contactwith the peripheral portion of the first solder bump, whereby the pairof leads are shorted. As a result, the circuit can be positively formedinto a closed circuit.

Also, in the circuit shorting method according to the present invention,the step of crushing the other solder bump is performed until a part ofthe peripheral portion of the other solder bump overlaps the peripheralportion of the first solder bump. Therefore, a contact area between thesolder bumps is increased and the leads can be positively shortedbetween them.

Further, in the circuit shorting method according to the presentinvention, the solder bumps are crushed while being softened underheating. Therefore, the load required for crushing the solder bumps isreduced and the solder bumps can be positively crushed without damagingthe circuit board itself.

Moreover, in the circuit shorting method according to the presentinvention, the solder bumps are crushed simultaneously while beingsoftened under heating. Therefore, the load required for crushing thesolder bumps is reduced and the solder bumps can be positively contactedwith each other even when they are crushed simultaneously. Damage of thecircuit board is therefore avoided at the time of crushing the solderbumps.

Additionally, in the circuit shorting method according to the presentinvention, the solder bumps are each crushed under heating and rubbing.Therefore, each solder bump is pressed or spread in the planar directionof the circuit board while being crushed, and the solder bumps can bemore positively contacted with each other.

In the magnetic head according to the present invention, a sliderincluding an MR magnetic head device is attached to a fore end of a loadbeam, the above-mentioned circuit board is attached to an opposite endof the load beam, and a pair of lead lines extended from the MR magnetichead device are connected to the circuit board. The MR magnetic headdevice, the lead lines and the leads cooperate to construct or form acircuit. A pair of solder bumps connected to the leads are then crushedsuccessively to be contacted with each other, whereby the leads areshorted together or between them and the circuit is formed into a closedcircuit. As a result, the MR magnetic head device can be protectedagainst electrostatic breakdown.

Also, the magnetic head according to the present invention includes acircuit board which comprises at least a solder bridge for electricallyinterconnecting lands connected to the leads, the solder bridge beingformed by peripheral portions of the solder bumps formed respectively onthe leads and overlapped with each other. Therefore, the contact areabetween the solder bumps is increased and the leads can be positivelyshorted together or between them so that the circuit including the MRmagnetic head device is formed into a closed circuit.

In addition, since the peripheral portions of the solder bumps areoverlapped with each other, separation of the solder bumps is avoided,for example, even when the circuit board is bent. Therefore, the shortedstate between the leads established by the solder bridge is maintainedto prevent electrostatic breakdown of the MR magnetic head device, andreliability of the circuit board can be increased.

Furthermore, with the method of manufacturing a magnetic head accordingto the present invention, the circuit including the MR magnetic headdevice can be easily formed into a closed circuit by merely crushing thesolder bumps, and the MR magnetic head device can be protected againstelectrostatic breakdown.

What is claimed is:
 1. A circuit board comprising at least a pair ofleads for constructing a circuit, lands connected respectively to saidpair of leads, and solder bumps formed respectively on said lands,wherein a center-to-center distance between said solder bumps is in arange of 0.39 to 0.41 mm, said solder bumps are crushed, and peripheralportions of said solder bumps are spread to overlap with each other. 2.The circuit board according to claim 1, wherein each of the solder bumpshas a diameter of 0.29 to 0.34 mm.
 3. The circuit board according toclaim 1, further comprising a mounting terminal and an inspectionterminal formed on the same surface of the circuit board on which thesolder bumps are formed, wherein one end of each lead is connected to anelement; the mounting terminal is disposed between the element and thesolder bumps; and the inspection terminal is formed remote from themounting terminal.
 4. A circuit board comprising at least a pair ofleads for constructing a circuit, lands connected respectively to saidpair of leads, and solder bumps formed respectively on said lands,wherein a peripheral portion of one of said solder bumps overlaps aperipheral portion of the other solder bump, thereby connecting thesolder bumps with each other.
 5. The circuit board according to claim 2,further comprising a mounting terminal and an inspection terminal formedon the same surface of the circuit board on which the solder bumps areformed, wherein one end of each lead is connected to an element; themounting terminal is disposed between the element and the solder bumps;and the inspection terminal is formed remote from the mounting terminal.